The purpose of the above-cited flaps, which extend at least along the instep and are adapted to be superimposed upon each other, is to take up and distribute the forces originating at the moment the boot is tightly closed and fastened onto the wearer's foot. In addition, they are of course intended to prevent snow from penetrating into the boot itself.
Owing to the fact that the wearer's foot may be introduced into a ski boot or extracted therefrom even under prevailing conditions of quite low temperatures, e.g. outside on the skiing ground, the details concerning the opening where said flaps are provided are of a major consideration when designing a new boot model.
Then, since the flaps are usually moulded integrally as a unitary piece with the shell and leg-piece of the boot, respectively, and must be capable of most easily open apart even under the conditions of quite low temperatures, the flaps are designed as very thin parts, i.e. parts with a reduced thickness which represent a weak point in the construction of a boot.
A first solution to such problem is known from DE-A-198 15 344; this solution envisages the use of strips of textile material as hinges for connecting the flaps to the rest of the lower and upper shell, respectively. Notwithstanding the use of textile materials of a high tensile strength and impermeability to water (e.g., plastics-impregnated textiles), it can be reasonably expected that—at least after a more or less extended period of use of the boot—the flaps will structurally undergo a certain extent of yielding that will prevent them from closing in a uniform manner the opening of the boot.
Another solution, known from U.S. Pat. No. 5,553,401, envisages to make the flaps as parts to be moulded separately from the leg-piece and the shell of the boot and, as a result, loose, i.e. disengaged from the means (levers and racks) used to fasten the boot. Each flap has a lower or concealed portion that is moulded integrally as a unitary piece with an upper or exposed portion (which distributes the pressure originated and imposed by the fastening means) to which is connected via a thin-film hinge. Said upper portion of the flap opens and closes with a transverse movement for permitting the foot to slip into and out of the boot, whereas the lower portion is secured by means of a bolt to shell of the boot and is able to slide in the longitudinal direction of the boot. Quite clearly, due to the repeated flexural stresses they are going to be subject to, thin-film hinges represent weak points of the boot.
A third solution, known from WO-A-03 001937, envisages the use of panels in the form of real lids connected to the shell and/or the leg-piece of a ski by metal book-like (flat) hinges. Anyway, even this kind of hinges represents a critical aspect in the boot design, especially when the hinges need to be replaced; they furthermore are relatively expensive parts.
At last, from EP-A-551 881 a footwear for ski is known which comprises one or more interchangeable flaps removably associable with the quarter (leg-piece) and/or with the shell through rivets integrally formed with the flaps.